ATOMIC-SCALE THEORY OF RADIATION-INDUCED PHENOMENA Sokrates T. Pantelides Department of Physics and Astronomy, Vanderbilt University, Nashville, TN and Oak Ridge National Laboratory, Oak Ridge, TN The theory team: Matt Beck, Leonidas Tsetseris, George Hadjisavvas, Sasha Batyrev, Ryan Hatcher, Blair Tuttle AFOSR/MURI REVIEW 2007 In collaboration with the rest of the MURI team

THEORY OBJECTIVES DISPLACEMENT DAMAGE  Defects, charging  electrons ALTERNATE DIELECTRICS  Interface structure, interface defects, NBTI,… CARRIER MOBILITIES LEAKAGE CURRENTS FROM ATOMIC-SCALE PHYSICS TO ENGINEERING MODELS

Atomic-scale physics: DENSITY FUNCTIONAL THEORY PSEUDOPOTENTIALS, SUPERCELLS TOTAL ENERGY, FORCES ON ATOMS o Stable defect configurations o Bulk, interface o Reaction energies, activation barriers EVOLUTION OF SYSTEM electrons in instantaneous ground state vs electrons allowed to evolve freely BULK – INTERFACE CHARGING

THEORY OBJECTIVES DISPLACEMENT DAMAGE  Defects, charging  electrons ALTERNATE DIELECTRICS  Interface structure, interface defects, NBTI,… CARRIER MOBILITIES LEAKAGE CURRENTS FROM ATOMIC-SCALE PHYSICS TO ENGINEERING MODELS TALK BY A. MARINOPOULOS

8 Å Van Benthem & Pennycook, ORNL

H + H + Si Hf H + suboxide Si-sub SiO 2 HfO 2 bond H NEGATIVE BIAS H + H + Si Hf H + suboxide Si-sub SiO 2 HfO 2 bond H Si-SON-HfO 2 Vanderbilt team POST-IRRADIATION SWITCH-BIAS ANNEALING

THEORY OBJECTIVES DISPLACEMENT DAMAGE  Defects, charging  electrons ALTERNATE DIELECTRICS  Interface structure, interface defects, NBTI,… CARRIER MOBILITIES LEAKAGE CURRENTS FROM ATOMIC-SCALE PHYSICS TO ENGINEERING MODELS TALK BY A. MARINOPOULOS TALK BY M. BECK

A Displacement Single Event How does energy translate to electrical activity ?

Red (hot) atoms: KE > 0.22 eV Black atoms: displaced > 0.2 Å 25 eV kick Snapshot after 100 fs

THEORY OBJECTIVES DISPLACEMENT DAMAGE  Defects, charging  electrons ALTERNATE DIELECTRICS  Interface structure, interface defects, NBTI,… CARRIER MOBILITIES LEAKAGE CURRENTS FROM ATOMIC-SCALE PHYSICS TO ENGINEERING MODELS TALK BY A. MARINOPOULOS TALK BY M. BECK TALK BY I. BATYREV

PSG Al 7*10 17 cm -3 3*10 17 cm -3 6*10 15 cm -3 3*10 15 cm -3 SiO % H 2 CBE μmμm μmμm

THEORY OBJECTIVES DISPLACEMENT DAMAGE  Defects, charging  electrons ALTERNATE DIELECTRICS  Interface structure, interface defects, NBTI,… CARRIER MOBILITIES LEAKAGE CURRENTS FROM ATOMIC-SCALE PHYSICS TO ENGINEERING MODELS TALK BY A. MARINOPOULOS TALK BY M. BECK TALK BY I. BATYREV PLUS SOMETHING SPECIAL

Universal mobility 4 NOT ANY MORE

Strained n-type Si p type Si oxide “metal” Strained-Si Bulk MOSFET K. Rim, J. L. Hoyt, and J. F. Gibbons (2000) Fischetti et al. 2002: fit data with unusually low interface roughness

ALL MOBILITY CALCULATIONS SUPPRESS ATOMIC-SCALE DETAIL SiSiO 2 V(z) ~30-100≤ EFFECTIVE-MASS THEORY BULK ENERGY BANDS INFINITE POTENTIAL BARRIER FREE PARAMETERS

ATOMIC-SCALE SIMULATIONS p type Si oxide “metal” SOI MOSFET

Scattering Potential V ideal V defect  V = V defect - V ideal

SiSiO 2 OXYGEN PROTRUSION SiSiO 2 SUBOXIDE BOND ATOMIC-SCALE ROUGHNESS

Enhancement factor  ~ N def for each defect

Mobility Enhancement Data from bulk MOSFETs or SOI MOSFETs with t>5 nm

Z-contrast image -- Si-SiO 2 interface SiO 2 Si Image by Pennycook et al. WHAT CONTROLS THE ABRUPTNESS OF THE Si-SiO 2 INTERFACE?

SiO 2 Si 1. Why so abrupt?Si-Si in silicon = 2.35 Å Si-O-Si in SiO 2 = 3.1 Å (~400ºC) (~100ºC) (~3.5 eV)2. Why T ox > 800ºC ? E a = 1.2 eV Oxidation time (hours) Oxide thickness (  m) E a = 2 eV Deal and Grove, 1965

Si SiO 2 Diffusion activation energies E A = 1.2 eV E A = 2.0 eV

(4) (3) 3Å3Å Thermal oxidation: a random “deposition” process? Analogy with film growth: where O 2 lands, it sticks Barabasi and Stanley, “Fractal Concepts in Surface Growth”

“Reorganization” at the Si-SiO 2 interface (a) (b) Gain in energy ~ 1-2 eV → smoother interface Relaxation barrier ~ 2.1 eV Lateral diffusion barrier ~2.1 – 2.3 eV

Random deposition “Fractal Concepts in Surface Growth”, Barabasi and Stanley Random deposition with relaxation

Still, why do you need 800ºC to get a smooth interface? O diffusion in Si E a = 2.3 eV But, binding of O to interface E ~ 1.0 eV “Desorption enhanced lateral diffusion” E a ~3.3 eV ! That’s the 800ºC !

“Reorganization” at the Si-SiO 2 interface (a) (b) Gain in energy ~ 1-2 eV → smoother interface Relaxation barrier ~ 2.1 eV Lateral diffusion barrier ~2.1 – 2.3 eV Desorption-enahnced lateral diffusion barrier ~3.3 eV